Molded plastic dispensing closures, that can be integrally molded, have met with widespread commercial acceptance for dispensing products too diverse to enumerate and/or categorize. Known dispensing closures usually include a closure body that is secured to the neck of the container holding the product to be dispensed or discharged, and a lid that can be pivoted between an open, or discharging position, and a closed position. A "living" hinge is frequently integrally molded with the lid and the closure body from a polymeric plastic, and the "living" hinge enables the lid to be pivoted relative to the closure for the life expectancy of the closure.
While the dispensing closures described supra function satisfactorily under most conditions, the "living" hinges occasionally fail structurally or do not function satisfactorily. Such problems with the living hinges, which are but a few thousandths of an inch in thickness, have caused the closure industry to look for more effective ways of stressing, and/or operating, the "living" hinges.
Other problems have been encountered with known dispensing closures utilizing "living" hinges. In many instances, the hinge is formed as a bell-crank with one end secured to the rear surface of the closure body and the other end secured to the central area of the lid. A notch is cut out of the lid to allow the hinge to flex properly. When the lid is pivoted into its closed position, one leg of the bell-crank fits within the notch, leaving a small clearance therebetween. The small clearance, while necessary for the successful operation of the "living" hinge, provides a discontinuous upper surface for the lid. Dirt, dust, residue of the product being dispensed, and other foreign materials can accumulate in the clearance and create an unsightly appearance. Since the dispensing closures are frequently used on containers for hair care products, nail care products, foodstuffs, and other products which require an aesthetically pleasing, and almost sterile appearance, the discontinuities in the surface of the lid have proven to be a consistently negative factor.
Furthermore, in some instances, the lid secured by the "living" hinge to the closure body has sagged inwardly. The sag in the lid is unsightly, and detracts from the visual appearance of the dispensing cap; also, the sag provides a place for dirt and dust to accumulate during the shelf-life of the container upon which the dispensing closure is seated.
In order to properly stress the "living" hinge of known closures as the lid is pivoted between its opened and closed positions, diverse camming mechanisms have been utilized. For example, as shown in U.S. Pat. No. 4,220,248, granted Sept. 2, 1980 to W. S. Wilson and R. E. Hazard, upstanding resilient posts (50) project upwardly from the upper surface of the closure body and coact with cams, or camming surfaces (52), defined at the lower edge of the skirt of the lid. The cams contact and deform the posts during movement of the lid, and enhance the successful operation of the closure. A similar camming action is achieved by cooperating, dissimilarly oriented posts or tabs situated on the top surface of the closure body and the underside of the lid, as shown in U.S. Pat. No. 4,158,902, granted in June 1979, to Milton Chernack et al.
Employing upstanding posts, or tabs, for coaction with camming surfaces defined on the lid successfully assisted the operation of the "living" hinge utilized in the dispensing closures. However, posts and tabs proved to be difficult to mold accurately, and such upstanding projections frequently interfered with the high speed capping machines used to secure the dispensing closures atop containers. Also, the posts and tabs presented surfaces about which dirt, dust, product residue, and the like could easily accumulate. Consequently, dispensing closure of this type have met with limited commercial success and consumer acceptance.
Several other dispensing closures have been designed to provide a camming action that will enhance the operation of the "living" hinge employed within such closures. One known dispensing closure of particular interest is shown in U.S. Pat. No. 4,377,247, granted Mar. 22, 1983, to Robert E. Hazard and Woodrow S. Wilson. This patent is assigned to Polytop Corporation of Slatersville, R. I. the corporate assignee of the present application.
The dispensing closure depicted in the Hazard et al patent provides a camming action by virtue of the engagement of lower edges (52) on the skirt of the lid engaging the flat wall (22) formed on the upper surface of the closure body, and in the vicinity of the hinge (16). The closure body is sealed by a sloping top that includes the flat wall, and a holder (32) is formed to locate the "living" hinge so that the lid and closure body are joined together. While this dispensing closure has met with commercial acceptance, has good visual appeal, and has functioned satisfactorily on a variety of containers, such closure utilizes a relatively long skirt on the lid and thus is difficult to mold and to remove from the mold. Consequently, a parting line is visible on the skirt of the closure; also, such closure requires costly tools and dies in order to manufacture same on a commercially feasible basis.